1. Field of the Invention
The present invention relates generally to the field of volumetrically measuring the flow of fluids through a conduit and, more particularly, to an adjustable ball-type follower flowmeter which can be readily calibrated to a standard curve.
2. Description of the Prior Art
The prior art is repleat with numerous types of flowmetering devices for measuring the flow of fluids through pipelines or the like. Many of these flowmeters either utilize some type of spinning element or a follower element such as a ball which follows a track. In meters employing a spinning element, typically the element includes several arms or paddles which interact with the fluid flowing through the meter to produce rotation of the element. The rate of rotation is measured as a function of the flow rate through the meter. Such devices are expensive, difficult to assemble, and are subject to a great deal of maintenance because of the complex element structure including the necessity for a low friction mounting in the housing.
Follower element flowmeters of the ball type are also generally known in the prior art. These devices usually have a housing containing a ball race in the form of a circular toroidal cavity having fixed inlet and outlet ports which may be tangential to the race and through which all of the fluid to be measured flows. The ball is driven along the path by the fluid and the passage of the ball is sensed at one or more fixed points along the path. The speed at which the ball travels or revolves is proportional to the volume rate of fluid flow through the meter and thus the frequency at which the ball passes the sensing point or points is also proportional to the volume rate of flow through the meter. Because the fluid volume displaced between sensing points is known, each sensing of the ball defines a known incremental fluid volume which can be used to determine the total volumetric flow rate.
One example of such a device is shown in U.S. Pat. No. 4,157,660. That device has tangential inlet and outlet ports in opposed relationship on opposite sides of the toroid and a single photoelectric or magnetic pickup device to detect the frequency of revolution of the ball. In order to achieve accuracy over a range of flow rates with that device, the inlet flow is provided with a metering orifice and if flow is to be measured in either direction, both the inlet and the outlet ports must be provided with a metering orifice.
Another prior art device is shown in U.S. Pat. No. 4,203,323. That device utilizes a plurality of sensors along the path to decrease the incremental volume and therefore increase the accuracy of the incremental volume measured. In addition, to overcome inherent non-linearities in that device, a programmed memory unit is provided which compares the signal repetition rate with stored data representing the fluid volume passing through the flowmeter per signal as a function of the signal repetition rate to produce the correct volume flow rate in accordance with a previous calibration.
As can be seen from the above, the basic premise of the follower-element flowmeter is that there be a direct linear proportionality between the volume flow rate and the rotational repetition of the follower element over the range of flow rates sought to be measured. In reality, certain configurations appear to be more linear than others and within a group of meters of a given type, the accuracy may depend upon the repeatable precision of parts and assembly. As can be seen from the prior art cited, much of the innovation in a field has been directed toward overcoming various inaccuracies in the flowmeters which are present for known and unknown reasons.
The requirement of utilizing such devices as precise metering orifices or individually calibrated microprocessors to correct actual readings have been necessary. While these approaches generally increase the accuracy of the flowmeters, they increase the complexity and the cost of the flowmeters sometimes to the point where any advantage gained by the simplicity of the device may be lost.